This paper presents the results of an experimental program aimed at characterizing tube specimens from an estuarine soft clay deposit, which contains variable amounts of shells. The characterization of the natural clay involved two non-destructive techniques for assessing specimen quality, namely computed axial tomography (CAT) and shear wave propagation using bender elements, as well as one-dimensional consolidation tests for evaluating soil compressibility. Image analysis of CT scans was used to quantify the volumetric shell fraction and its influence on the compressibility parameters derived from one-dimensional compression tests. The experimental results show that both the compressibility and the small-strain stiffness of the natural soft clay are influenced by the volumetric shell fraction.